var xmlHttp = createXmlHttpRequestObject();

var updateInterval = 5; // how many seconds to wait to get new message

var errorRetryInterval = 30; // seconds to wait after server error

var debugMode = true;

var loader = "<div id='loader'><img src='images/loader.gif'></div>";

function createXmlHttpRequestObject() 
{
  var xmlHttp;
  try
  {
    xmlHttp = new XMLHttpRequest();
  }
  catch(e)
  {
    var XmlHttpVersions = new Array("MSXML2.XMLHTTP.6.0",
                                    "MSXML2.XMLHTTP.5.0",
                                    "MSXML2.XMLHTTP.4.0",
                                    "MSXML2.XMLHTTP.3.0",
                                    "MSXML2.XMLHTTP",
                                    "Microsoft.XMLHTTP");
    for (var i=0; i<XmlHttpVersions.length && !xmlHttp; i++) 
    {
      try 
      { 
        xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
      } 
      catch (e) {}
    }
  }
  if (!xmlHttp)
    alert("Error creating the XMLHttpRequest object.");
  else 
    return xmlHttp;
}

function display($message)
{
  myDiv = document.getElementById("news-menu");
  myDiv.innerHTML = $message;

}

function displayError($message)
{
  display("Error retrieving the news message! Will retry in " +  errorRetryInterval + " seconds." +  (debugMode ? "<br/>" + $message : ""));
}



function readnews(start)
{
  if (xmlHttp)
  {
    try
    {
      display(loader)
      xmlHttp.open("GET", "readnews.php?start=" + start, true);
      xmlHttp.onreadystatechange = handleGettingNews;
      xmlHttp.send(null);
    }
    catch(e)
    {
      displayError(e.toString());
    }
  }
}

function handleGettingNews() 
{
  if (xmlHttp.readyState == 4) 
  {
    if (xmlHttp.status == 200) 
    {
      try
      {
        getNews();
      }
      catch(e)
      {
        displayError(e.toString());
      }
    } 
    else
    {
      displayError(xmlHttp.statusText);   
    }
  }
}

function getNews()
{
  var response = xmlHttp.responseText;
  if (response.indexOf("ERRNO") >= 0 || response.indexOf("error") >= 0  || response.length == 0)
    throw(response.length == 0 ? "Server error." : response);
  display(response);
}

// popola i task di un contenuto interattivo

function get_path(id)
{
  if (xmlHttp)
  {
    try
    { 	 
      xmlHttp.open("GET", "getpath.php?id=" + id, true);
      xmlHttp.onreadystatechange = handleGettingPath;
      xmlHttp.send(null);
    }
    catch(e)
    {
      displayError(e.toString());
    }
  }
}

function handleGettingPath() 
{
  if (xmlHttp.readyState == 4) 
  {
    if (xmlHttp.status == 200) 
    {
      try
      {
        getPath();
      }
      catch(e)
      {
        displayError(e.toString());
      }
    } 
    else
    {
      displayError(xmlHttp.statusText);   
    }
  }
}

function getPath()
{
    var response = xmlHttp.responseText;
  if (response.indexOf("ERRNO") >= 0 || response.indexOf("error") >= 0  || response.length == 0)
    throw(response.length == 0 ? "Server error." : response);
  display(response);

}